Noble metal catalysts supported on a variety of porous supports have been used in the many processes, such as hydrogenation, dehydrogenation, cyclization, and various hydrocarbon conversion processes.
In general, the supported noble metal catalysts have been prepared by a variety of means such as coprecipitation with the support such as alumina, followed by washing, drying, calcining. Alternatively, the support is first formed in any of a variety of shapes, and the porous support then impregnated with an aqueous solution of a noble metal compound, such as chloroplatinic acid, and the resulting composite dried, and calcined. Other methods of impregnation have been employed, other than aqueous impregnation, such as the use of nonaqueous media.
The art methods have provided highly effective catalysts, though these catalysts in general have been a product in which only a portion of the catalysts, that is, the noble metal, has been available for active duty. The active portion of the noble metal normally is that which is on the surface. Noble metal which is deep inside the support is substantially wasted. As costs of noble metals have increased, so have costs of the catalysts. Needed are methods of providing highly active catalysts with only fractional contents of noble metal, yet which will exhibit sufficient activity. Most vitally needed are supported noble metal catalysts in which substantially all of the noble metal is at the surface, available for active participation in the catalytic processes, and not otherwise being wasted by being buried in the body of the catalysts.